Are you talking about adding a new point of intrest to the map data, or adding a new type of icon to the main mapnik layer, the osmarender layer, the potlatch2 editor, JOSM editor or any other programs/renderings that uses OSM data?

If you want to have additional icons on a map, you can either make your own map or try to convince the maker of the map in question to add this feature. For the "official" OSM map (mapnik) the way to go would be file a ticket in trac and hope that the makers agree to your idea.

Please take into account that it is impossible to fulfill all requests, because this would clutter the map until it became useless. It is always necessary to choose some features out of all data (thereby omitting others).

You may also add the ticket for osmarender layer (it is the layer where practically everything gets rendered). You can later choose the osmarender layer by clicking on plus sign on the upper right corner of the main map.